This section is intended to provide a background or context to the invention disclosed below. The description herein may include concepts that could be pursued, but are not necessarily ones that have been previously conceived, implemented or described. Therefore, unless otherwise explicitly indicated herein, what is described in this section is not prior art to the description in this application and is not admitted to be prior art by inclusion in this section. Abbreviations that may be found in the specification and/or the drawing figures are defined below at the end of the specification but prior to the claims.
Device-to-device (D2D) communications allow wireless devices, typically referred to as UEs, to communicate with each other directly. In D2D communications, UEs transmit data signals to each other over a direct link using cellular resources instead of having to communicate through a base station (such as an eNB). Typically, D2D users communicate directly while the base station retains control of the UEs and their communications.
There is a feasibility study on Proximity-based Services (ProSe) for D2D, which has identified services that could be provided by a 3GPP system based on UEs being in proximity to each other. See, e.g., 3GPP TR 22.803 V12.2.0 (2013-06). The objective is to study use cases and identify potential requirements for operator network controlled discovery and communications between UEs that are in proximity, under continuous network control, and under 3GPP network coverage. The identified areas include services related to commercial services and public safety that would be of interest to operators and users.
An additional feasibility study has objectives such as to evaluate LTE device-to-device proximity services, both within and outside network coverage. For instance, within network coverage, discovery could be performed for non-public safety and public safety requirements, and direct communication could be performed at least for public safety requirements. See, e.g., 3GPP TR 36.843 V0.3.1 (2013-11).
Various options have been discussed for performing discovery and the corresponding direct communication that follows discovery for D2D. However, the current options for discovery may be improved.